Fin tooling can be described as a plurality of stacked plates having cutting and forming teeth on their periphery. Prior approaches leave unsatisfied a need for an improved plate construction that takes advantage of certain characteristics common in nonferrous materials. Typical patents showing rolls used for making fins with louvers are shown in U.S. Pat. Nos. 3,214,954; 3,318,128; 3,998,600; and 4,067,219.
The heat exchange industry has rapidly changed from producing copper/brass heat exchangers to aluminum heat exchangers utilizing fin strips. This change has occurred primarily to take advantage of the weight reduction aluminum offers. The aluminum strips can be bonded by several braze methods such as vacuum brazing, flux brazing, and controlled atmosphere brazing to name a few. In recent years controlled atmosphere brazing (CAB) has become a brazing method of choice. The CAB process requires the use of clad aluminum alloys on the aluminum strip that is subsequently formed into fins. The clad is made up of 5-7% silicon, ranging in thickness from 1% to 10% of the total material thickness. This clad typically covers one or both sides of a base aluminum alloy. Silicon is best known for its abrasive qualities and these tendencies are the same when used as a cladding for fin material.
Consequently, fin rolls produced from the standard hardened steel plates wear much more rapidly when silicon clad aluminum fin material is formed than when non clad aluminum or copper fin materials are formed. This problem is most severe in fin rolls for making fins with louvers. Although this problem has long existed, the problem has not been solved by prior approaches.
Current steel roll technology is limited by the hardness that can be achieved through known heat treating processes. Significant hardness can be achieved with steel but at the expense of losing other desirable properties such as ductility and crack resistance. It is desirable to produce fin rolls with the hardest available material in order to enhance the bearing effectiveness, i.e., the ratio of soft to hard is directly related to the amount of friction created. This may reduce the amount of oil consumed during the forming process.
Steel rolls secondly have the tendency to corrode due to dissimilar metals in combination with numerous combinations of lubricants used in the fin forming process. Once corrosion begins, the pitting areas will rapidly diminish the roll's ability to make clean cuts and forms to the tolerances required for optimal heat exchanger performance. Steel rolls also become magnetized through repeated contact with each other. This magnetic field causes ferrous metal fines to cling to the rolls and consequently find their way to the sharp cutting surfaces. When these metal fines are sheared by the cutting surfaces, a dulling of the cutting surfaces occurs.
Finally, the grain structure and surface density of steel have an effect on the tendency of aluminum to attach itself to the steel roll surface. The smaller the grain structure and the denser the rolls' surface, the less galling occurs.